[IMPROVEMENT] Create Platform-Independent Paths

[smusali]

1. Understanding Path Differences Across Platforms: How directory and file paths are represented between operating systems. Hardcoding paths using one slash type can lead to errors when the code is run on a different operating system. For instance, Windows uses backslashes (\) to separate directories, while Unix-based systems like Linux and MacOS use forward slashes (/).
2. Utilize the file.path() Function: R provides the file.path() function designed to handle file path creation in a platform-independent way. It takes parts of a path as arguments and returns a string representing the path, using the appropriate slash for the current operating system. So, instead of hardcoding a path like "folder/subfolder/file", you should create the path using the file.path("folder", "subfolder", "file").
3. Avoid Hardcoding Absolute Paths:
   1. Hardcoding absolute paths can cause problems because the exact structure of the file system can differ between machines. For instance, the location of your project directory might not be the same on your machine and a collaborator's machine.
   2. Instead, use relative paths whenever possible. A relative path specifies the location of a file relative to the current working directory. For instance, if you have a file in a subdirectory of your project called "data", you can refer to it as the file.path("data", "file") without having to specify the full path to the "data" directory.
   3. When running tests or scripts, ensure the working directory is set to the project root. This way, all relative paths will be consistent regardless of the machine the code is run on.
4. Handle User-Specified Paths Correctly: If your package allows users to specify their file paths (for instance, as arguments to functions), handle these in a platform-independent way. Use file.path() to join parts of paths and the normalizePath() function to convert a path to a standard form for the current operating system.
5. Checking File and Directory Existence: When working with files and directories, checking whether they exist before using them is good practice. This can help prevent errors and give more straightforward error messages. The file.exists() function can check whether a file or directory exists, and dir.exists() can check specifically for directories.